1. Field of the Invention
This invention relates to a spray paint gun, more particularly to a spray paint gun which has a valve device for controlling the access of the compressed air into a paint container.
2. Description of the Related Art
Referring to FIG. 1, a conventional spray paint gun 1 includes an elongated gun body (1A) and a handle (1C) which is connected to a compressed air source (not shown). The gun body (1A) has a first air passage (1B) and a blind hole 4 extending longitudinally and inwardly from the front end of the gun body (1A). The first air passage (1B) is connected to the compressed air source via the handle (1C). Therefore, compressed air may be directed to the front end of the gun body (1A). A trigger 2 is provided pivotally on the gun body (1A) for controlling the air flow of the compressed air. An air cap (3A) with two air channels (3A') is mounted to the front end of the gun body (1A) by means of a screw nut (3B). An air chamber (3C) is formed between the front end of the gun body (1A) and the air cap (3A). The air chamber (3C) is communicated with the first air passage (1B). A nozzle 5 has a first end, which is threaded to the open end of the blind hole 4, and a tapered second end which is received in the air cap (3A). The nozzle 5 has a central through hole (5A) and a spray needle 1 received therein for opening and closing the central through hole of the nozzle 5, as best illustrated in FIG. 1A. A plurality of holes (5 C) are formed in the tapered second end of the nozzle 5, which communicate the air chamber (3C) and the exterior of the gun body (1A). A connecting portion 6 has an externally threaded lower section (6B) which depends from a lower portion of the connecting portion 6. The externally threaded lower section (6B) of the connecting portion 6 is connected threadedly to an upper end of a tubular member 7. A paint container (T) is threaded to a lower end of the tubular member 7. The connecting portion 6 has a through bore (6A) that is communicated with the blind hole 4 of the gun body (1A). A pipe member 8 has a first end, which is inserted into the through bore (6A), and a second end which extends through the tubular member 7 and into the container (T). A second air passage 9 extends through the gun body (1A) and the connecting portion 6 in order to interconnect the air chamber (3C) and the interior of the container (T). The second air passage 9 has an internally threaded section (9B) adjacent to the air chamber (3C) and an outlet (9A) adjacent to the interior of the tubular member 7. The lower end of the tubular member 7 has a threaded hole (7A) in which a stop screw (7B) is threaded.
When in use, the trigger 2 is actuated to allow compressed air to flow through the first air passage (1B) of the gun body (1A) and to the air chamber (3C). The compressed air flows out of the gun body (1A) from the air channels (3B') of the air cap (3A) and the holes (5C) of the nozzle 5, as best illustrated in FIG. A, which is an enlarged view of the encircled portion (A) in FIG. 1. A part of the compressed air flows into the paint container (T) via the second air passage 9. Thus, the internal pressure of the paint container (T) will be increased to a sufficient value, thereby forcing paint in the paint container (T) to enter the blind hole 4 through the pipe member 8 and the through bore (6A). The paint will further flow to the central through hole (5A) of the nozzle 5 and will be dispersed into mist by means of the compressed air which flows through the air channels (3B') of the air cap (3A) and the holes (5C) of the nozzle 5. Since the paint in the paint container (T) is directed to the blind hole 4 of the gun body (1A) by means of the compressed air, a thicker paint may be used for spray painting.
If a thinner paint is to be used for spraying painting, the paint may be siphoned from the paint container (T) to the central hole (5A) of the nozzle 5, as best illustrated in FIG. 2. In this situation, the compressed air should be prevented from entering the second air passage 9. This can be accomplished by removing the screw nut (3B), the air cap (3A) and the nozzle 5, in this sequence, from the front end of the gun body (1A). The stop screw (7B) is then threaded from the threaded hole (7A) and threaded into the internally threaded section (9B) of the second air passage 9. The nozzle 5, the air cap (3A) and the screw nut (3B) are mounted, in this sequence, to the front end of the gun body (1A). Thus, the compressed air will flow through the holes (5C) of the nozzle 5 and the air channels (3A') of the air cap (3A) and will not enter the second air passage 9. Therefore, the paint can be directed to the blind hole 4 and is released from the gun body (1A) by means of the pressurized air force or the siphon force by opening or closing the second air passage 9 with the use of the stop screw (7B).
The conventional spray paint gun has the following disadvantages:
(1) Insertion and removal of the stop screw (7B) into and from the threaded section (9B) are troublesome operations.
(2) Since the stop screw (7B) is very small (the outer diameter and the length of the stop screw (7B) are both about 3 mm), the stop screw (7B) is liable to miss and can be damaged when threaded in the threaded section (9B) of the second air passage 9.